In the welding of metal objects together, especially when an intentional gap is provided between the objects to be welded together to enable penetration of the weld completely through the depth of the object, a considerable amount of weld metal passes completely through the gap between the objects, this being known as "blow through". Not only is weld metal wasted because of blow through, but the weld is rendered unattractive and rough because of formation of "cat's whiskers" of weld metal at the backside of the weld, and other weld deformations. In the case of pipe sections welded together end-to-end, such roughness and irregularity of the weld at the inside of the pipes causes flow and corrosion problems which cannot be tolerated. Grinding or other finishing operations at the inner side of the weld must be performed before the pipeline can satisfactorily be used to convey petroleum products.
To improve the qualities of such welds in pipelines, and to avoid the cost and trouble of finishing operations, this invention provides methods and apparatus whereby welds can be formed which are of improved appearance and smoothness at the backsides of the welds.